Antiemetic classes:
AntihistamineEffective in conditions such as motion sickness, morning sickness in pregnancy, and opioid nausea. Cyclizine, Diphenhydramine, Meclozine, Promethazine.
BenzodiazepineAlso used for sedation, anxiety relief, muscle relaxation, anti-convulsion.Midazolam, Lorazepam
SteroidA low dose given at the onset of general anaesthetia. Dexamethasone
5-HT3 receptor antagonistsThese block serotonin receptors in the CNS and GI tract. Used to treat post-operative and cytotoxic drug nausea & vomiting.Dolasetron, Mirtazapine (antidepressant), Ondansetron

Example antiemetics...